构造粉化煤体双孔损伤突变点识别及瓦斯表观扩散分阶响应机制

The rapid desorption of gas from powdery tectonic coal is an essential condition when an outburst occurs and develops. However, the gas desorption law will show a sudden change when the coal is subjected to different forces. As the particle size becomes smaller than a critical value, a sudden increase appears in the initial desorption rate, eventually changing the whole curve shape of desorption. This study will take the tectonic coal as the research object and use the novel method of gas diffusion experiments in restricted environments. First, the pore damage path and the physical origin of the critical mutation point will be measured via multi-scale experiments. Then, with the mathematical methods of limit approximation, variable substitution and variable separation, a Fickian diffusion model containing pore geometric parameters will be established. In addition, a critical ratio will be deduced to describe the point that two systems exert equal influence in desorption, which will help evaluate the influence of the source-valve competitive relation of pores and fracture systems on the apparent gas diffusion curves. At last, based on the analysis of transport pattern evolution law in desorption, a mathematic model that can describe multi-flow in multi-shape space will be established. Based on the analysis above, a simple gas desorption model with high accuracy will be deduced and applied into the determination of outburst indexes. In addition, a staged energy instability model for outbursts will be obtained as well, which will provide a theoretical guidance for the accurate zoning of outburst areas.

构造粉化煤体中高速解吸的瓦斯流是突出发生及发展的必要条件。而瓦斯的解吸对于力学破坏常产生突变分阶的响应特征，表现为在某一临界粒径以下瓦斯解吸速度才会突然增高，解吸表观扩散曲线形态随之剧烈改变。本项目以构造煤为研究对象，采用原位受限条件煤体瓦斯扩散动力学实验等创新研究方法，首先获得构造粉化煤体理化性质的损伤路径，揭示解吸突变临界点的物理成因；之后利用极限近似、变量替换、分离变量及傅里叶变换等数学方法，建立含孔隙几何特征参数的表观菲克扩散动力学模型，进而获得孔隙裂隙传质主控角色转换的临界特征比值，探讨孔隙裂隙“源-阀”互抑作用对瓦斯表观扩散曲线的影响机制；然后通过分析损伤过程中瓦斯解吸主控传质方式的演化过程，建立可表征多种传质形式及多重空间损伤特征的解吸动力学模型；最终形成高精度解吸指标适配模型和基于粒径的突出能量失稳分阶模型，为防突工作提供理论指导。

煤粒瓦斯解吸速度在某一粒度之下会产生突变，使得解吸表观扩散曲线形态随之剧烈改变，为突出瓦斯膨胀能的迅速产生提供了条件。本项目首先绘制出了采动碎裂过程中煤体孔隙损伤的基本路径，获得了孔隙裂隙流动主控角色转换临界特征比值，明确了各解吸曲线形态差异化的主控因素，建立了含孔隙几何特征的表观菲克扩散动力学模型，构建了可表征多种传质形式、多重空间损伤特征的解吸动力学模型。主要研究结果如下：1）粉化破碎过程中，孔裂隙会经过三个阶段：①完整煤粒分裂成多个小粒径的新生煤粒；②单个煤粒继续破碎成为基质大小的煤粒，是瓦斯解吸速度极速增长的起点；③煤粒继续破碎，孔隙系统遭到严重破坏，瓦斯解吸速度极速增长。2）随着粒径减小，孔隙裂隙主控渗透率存在临界特征比值κ，其范围在0.1~0.001之间。当km/kf＞κ时，流动主控因素是裂隙流动，此区域的解吸曲线呈现低速、长时间的特征；当km/kf<κ时，流动主控因素是基质扩散，在此区域内解吸曲线呈现短时间内达到较高解吸质量，解吸速度大的特征。3）随着时间推移，瓦斯解吸过程分为游离瓦斯流动主控阶段、过渡阶段和基质吸附瓦斯扩散主控阶段。其中瓦斯曲线在游离瓦斯流动主控阶段和基质吸附瓦斯扩散主控阶段分别符合线性和单孔扩散模型规律。4）根据自扩散系数、修正扩散系数与菲克扩散系数的数学转换关系，得出了类自扩散系数时变规律的菲克扩散系数时变模型，进而将其引入经典的单孔模型中，最终获得了能反映孔隙结构参数变化的单孔扩散优化模型。5）在同等压力差条件下，裂隙主控和基质主控两类曲线抽采浓度提升效果不同。对于“高-低-高”、“低-高-低”，“同高或同低”等不同渗透率组合形式的煤层而言，应在低表观渗透率区域加大抽采时间、增强抽采负压、缩小抽采间距等方法，或采用水力化措施等强化抽采措施。项目成果可为突出指标的精确化厘定以及瓦斯精准抽采提供理论指导。